Description

The Sea Otter is the largest member of family Mustelidae, and the smallest marine mammal. Sea Otters are more aquatic even than seals and sea lions, because they mate and give birth in the water. They are tool users, using rocks to pound open hard-shelled prey, such as abalone. Once hunted almost to extinction for their fur, but now protected, they have made a comeback. This has stirred controversy where their predation on abalone, crabs, clams, and sea urchins affects shellfisheries. Ecologists are beginning to understand the larger, long-term role they play in shaping the marine environment, by eating creatures such as sea urchins. Sea urchins feed on and if unchecked, can destroy kelp. Vast underwater kelp forests are at the base of the coastal food web and also provide shelter for countless organisms.

Adaptation: In the sea otter (Enhydra lutris), adaptations to crushing marine invertebrates mark the skull through its powerful chewing muscles, which leave muscles scars in the form of raised ridges of bone and a rough surface texture. Note also the large, flat cheek teeth.

Biology

Highly aquatic, the sea otter rarely comes ashore, both resting and feeding in coastal waters. Alaskan sea otters are more at home out of the water than their Californian relatives, often hauling out on sandbars and ice (8). Otters have a high metabolic rate (9) and these resourceful, opportunistic predators need to consume 25 percent of their body weight a day (6). Diving to depths of up to 75 metres they retrieve invertebrates such as mussels, snails, crabs and urchins from the seabed (6). Pouches of skin at the armpit of each forelimb can be used to store food whilst it is carried to the surface (6). Otters float on their backs, using their chest as a table whilst they attempt to prize open the shells. Sometimes rocks are used to smash open the hard shells and sea otters are one of the only mammals (apart from primates) to have developed tool use (6). Sea otters are considered a 'keystone species' in some parts of their range, as they appear to be vital in the maintenance of kelp forest ecosystems by suppressing the number of sea urchins that would otherwise overgraze the forests (4). These gregarious creatures can be found in large same-sex groups known as 'rafts'. Rafts in California rarely exceed 50 individuals but in Alaska, where the population density is higher, up to 2,000 otters can gather (2). Sea otters probably spend more time and energy grooming their fur that any other mammal; an important activity required to maintain the insulation of their fur, as it cleans and replenishes air to the under fur (4). Grooming involves rubbing, rolling and blowing air into the fur (4). Trapped air in the under fur is heated by the body to provide insulation and gives otters a silvery appearance underwater (5). Sea otters are polygynous, with adult males generally defending territories that encompass the ranges of several females (2) (4). While mating, the male will grip the female's nose with his teeth and she is often left with a bloody souvenir of their encounter (4). Females usually give birth to a single pup and carry them on their chest, nursing them and grooming them meticulously to ensure the fur remains buoyant and insulated (9). Young pups are left on the surface whilst their mother dives for food, but as they mature they follow her, learning to forage by watching her technique (5). Pups will stay with their mother for around three to six moths (6).

Description

The sea otter, the smallest marine mammal in the world, is well adapted for its predominately aquatic lifestyle, possessing a strong, rudder-like tail and large hind-feet that act as flippers (2). Unlike other marine mammals, sea otters do not have blubber and instead rely on their fur to keep warm in the water (4); their reddish-brown coat is the densest of any mammal, consisting of around 100,000 hairs per cm² (2). The natural oils produced by the fur provide a waterproof quality (5).

Range Description

Historically, Sea Otters occurred across the North Pacific Rim, ranging from Hokkaido, Japan, through the Kuril Islands, the Kamchatka Peninsula, the Commander Islands, the Aleutian Islands, peninsular and south coastal Alaska and south to Baja California, Mexico (Kenyon 1969). In the early 1700s, the worldwide population was estimated to be between 150,000 (Kenyon 1969) and 300,000 individuals (Johnson 1982). Although it appears that harvests periodically led to local reductions of Sea Otters (Simenstad et al. 1978), the species remained abundant throughout its range until the mid-1700s. Following the arrival in Alaska of Russian explorers in 1741, extensive commercial harvest of Sea Otters over the next 150 years resulted in the near extirpation of the species. When Sea Otters were afforded protection by the International Fur Seal Treaty in 1911, probably fewer than 2,000 animals remained in 13 remnant colonies (Kenyon 1969). Remnant populations were located in the Kuril Islands, Kamchatka and in the Commander Islands Russia; five in Southwestern Alaska (the Aleutian Islands, Alaska Peninsula, and Kodiak Island), and one remnant population in each of the following regions; Southcentral Alaska (Prince William Sound), Canada (Queen Charlotte Islands), central California, and Mexico (San Benito Islands) (Estes 1980). However, the Queen Charlotte, Canada and San Benito Island, Mexico remnant Sea Otter populations have presumably died out and likely did not contribute to the recolonization of the species following near extirpation (Kenyon 1969).

In north America, the Sea Ottes range is fairly continuous from the Aleutian Islands to Prince William Sound with population gaps along the Gulf of Alaska until Yakutat (which was a translocated population) with another gap in the population’s distribution until the outer islands of Southeast Alaska (also a translocated population form the Aleutian Islands and Prince William Sound). The next gap in the Sea Otter population distribution is between Southeast Alaska and British Columbia, Canada. Translocation efforts were successful in Washington State but not in Oregon thus there is a large population gap between the small Sea Otter population in Washington and that of central California.

Geographic Range

Past distribution of the sea otter included Hokkaido Island of Japan north through the Kuril Islands and eastern coast of Kamchatka, east through the Commander Islands and Aleutian archipelago, the southern coast of Alaska, and the west coast of North America to Baja, Mexico. Sea ice limits their northern range to below 57 degrees N lattitude, and the distribution of kelp forests limits the southern range to about 22 degrees N lattitude. Hunting during the 18th and 19th centuries greatly reduced the distribution fo the sea otter. Three subspecies of Enhydra lutris are recognized today. E.l. lutris ranges from the Kuril Islands north to the commander islands in the western pacific. E.l. nereis is found off the coast of central California. E.l. kenyoni is distributed throughout the Aleutian Islands and southern Alaska, and has been reintroduced to various locations from south of Prince William Sound, Alaska to Oregon.

Range

Historically, the sea otter was found in coastal areas throughout the North Pacific (6). Sea otters can still be found in much of this former range although numbers are greatly reduced and populations fragmented (6). Three subspecies are currently recognised: the southern, or California sea otter (Enhydra lutris nereis), occurs from California to Mexico; the northern, or Alaskan sea otter (E. l. kenyoni), is found along the northwest coast of North America and into Alaska; and the Russian sea otter (E. l. lutris) occurs in the western north Pacific (7). Alaska plays host to possibly as much as 90 percent of the world population of this species (6).

Physical Description

Sea otters are the largest member of the family Mustelidae. Males weigh 22 to 45 kg and are 1.2 to 1.5 m in length. Females are slightly smaller, weighing 14 to 33 kg and measuring 1 to 1.4 m in length. The tail comprises less than a third of the body length. The pelage is brown or reddish brown. Sea otter fur is the densest of all mammals, with about 100,000 hairs per square centimeter. Since sea otters do not have any insulating fat, the fur is responsible for maintaining warmth. The hind legs are long and the paws are broad, flat, and webbed. The forelimbs are short and have retractable claws. Sea otters are the only carnivorans with just 4 lower incisors. Females have two mammae.

Differs from pinnipeds in longer tail and much smaller forelimbs that are not flipperlike. Differs from the river otter in shorter tail and flipperlike hind feet. This is the only carnivore with 2 pairs of lower incisors (all others have 3 pairs).

Habitat and Ecology

Habitat and Ecology

Throughout their range, Sea Otters use a variety of near shore marine environments and 84% of foraging occurs in water ≤ 30m in depth (Bodkin et al. 2004) and throughout much of their range, foraging occurs within a kilometer of the shore. Their classic association is with rocky substrates supporting kelp beds, but they also frequent soft-sediment areas where kelp is absent (Riedman and Estes 1990, DeMaster et al. 1996, Burn and Doroff 2005). Kelp canopy is an important habitat component, used for foraging and resting (Riedman and Estes 1990). They are found most often in areas with protection from the most severe ocean winds, such as rocky coastlines, thick kelp forests, and barrier reefs. Although they are most strongly associated with rocky substrates, Sea Otters can also live in areas where the sea floor consists primarily of mud, sand, or silt. Individuals generally occupy a home range a few kilometers long, and remain there year-round. Sea Otters forage in rocky and soft-sediment communities on or near the ocean floor. The maximum confirmed depth of dive was 97 m (Newby 1975); however recent studies using time-depth recorders implanted in Sea Otters indicate average maximum forage depths of 54 m for female and 82m for male Sea Otters (Bodkin et al. 2004).

Sea Otters are weakly territorial (Kenyon 1969) with fighting and aggression rare (Loughlin 1980). Only adult male Sea Otters establish territories. Males patrol territorial boundaries and attempt to exclude other adult males from the area. Females move freely between and among male territories. Groups of male and female Sea Otters generally rest separately. Sea Otter annual home ranges can occupy up to 0.8 km² (80 ha) and extend along 16 km of coastline (Kenyon 1969, Loughlin 1980). Typically, female Sea Otter home ranges are about 1.5–2 times larger than resident adult males during the breeding season; however, females have smaller annual or lifetime home ranges than males (Riedman and Estes 1990). Jameson (1989) found that territorial adult males occupied a mean home range of 40.3 ha during the summer-fall period (when home range size was considered equal to territory size); and mean coastline length was 1.1 km. Winter-spring mean home range size of territorial adult males that remained in female areas was 78.0 ha, with a mean coastline length of 2.16 km.

The diet of Sea Otter consists almost exclusively of marine invertebrates, including sea urchins, a variety of bivalves such as clams and mussels, abalone, other molluscs, crustaceans, and snails. Its prey ranges in size from tiny limpets crabs and giant octopuses (Estes 1980). Sea urchins, abalones and rock crabs are the principal prey of Sea Otters in newly reoccupied habitats of central California (Vandevere, 1969) whereas clams and crab will make up the diet in soft-sediment habitats (Kvitek et al. 1992, Doroff and DeGange 1994). Where prey such as sea urchins, clams, and abalone are present in a range of sizes, Sea Otters tend to select larger items over smaller ones of similar type (Kvitek et al. 1992). In California, it has been noted that Sea Otters ignore Pismo clams smaller than 3 inches (7 cm) across. Only in the Aleutian archipelago were Sea Otters observed to regularly eat fish, which could comprise up to 50% of their diet. The fish species eaten were usually bottom dwelling and sedentary or sluggish forms, such as the Red Irish Lord and Globefish (Estes 1980). They also consume crab, clam, mussels, turban snails, sea cucumbers, squid, octopus, chitons, tubeworms, large barnacles, scallops, and sea stars (Wild and Ames 1974, Riedman and Estes 1990). Bivalve molluscs are excavated by digging in sand or mud bottoms and are the most common prey in soft-sediment communities (Calkins 1978, Kvitek et al. 1992, Doroff and DeGange 1994).

Male Sea Otters reach sexual maturity around age five or six, but probably do not become territorial or reproductively successful for two or three subsequent years (Riedman and Estes 1990). Most female Sea Otters are sexually mature at age four or five (Kenyon 1969, Jameson and Johnson 1993, Monson et al. 2000, Monson and DeGange 1995, von Biela 2007). Sea Otters apparently are polygynous, although the exact nature of the mating system may vary. Females normally give birth to a single pup that weighs 1.4 to 2.3 kg at birth (Riedman and Estes 1990). Twinning has been documented in Sea Otters (Williams et al. 1980); however, litters larger than one are rare, and when they occur, neither pup is likely to survive (Jameson and Bodkin 1986). Pups remain dependent upon their mothers for about six months (Jameson and Johnson 1993). Longevity in Sea Otters is estimated to be 15 to 20 years for females and 10 to 15 years for males (Riedman and Estes 1990).

Comments: Coastal waters usually within 2 km of shore, especially shallows with kelp beds and abundant shellfish. In rough weather, takes refuge among kelp, or in coves and inlets. Often comes ashore in Alaska, rarely does so in California. In California, juvenile males spend little time in near-shore kelp beds; often remain far offshore (Siniff and Ralls (1988). In California, young are born in the water or on land; births may usually occur ashore in Alaska.

Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.

Locally Migrant: Yes. At least some populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

Food Habits

Sea otters are carnivorous. They will eat nearly any seafood they can find in their kelp forest foraging grounds. Their diet consists of marine invertebrate herbivores and filter feeders such as mussels, sea urchins (Strongylocentrotus sp.), snails, and abalone. Otters also are known to eat crabs, octopus, squid, sea stars, and fish. Individuals tend to be specialized in their choice of prey: one otter may consume only urchins and crabs while another will eat mostly fish, all depending on the abilities of the individual otter and what is available in the area. Otters need to consume 20-25% of their body weight each day. They obtain most of their water from prey but will drink seawater to satisfy thirst also.

Comments: Diet varies according to location; often dominated by benthic invertebrates. Sea urchins, crabs, and a variety of molluscs are principal foods, but fish are important food items at high population densities. Forages usually at depths of less than 20 m. Uses rocks or other hard objects as tools to break exoskeletons of invertebrate prey. Diets and patterns of foraging behavior may be highly individualized (Riedman and Estes 1990).

Ecosystem Roles

Sea otters are a keystone species. They play a major role in the community by controling of herbivorous invertebrates, mainly the sea urchin (Strongylocentrotus sp.), inhabiting kelp forests. Sea urchins graze on kelp. In coastal areas where otters are absent, sea urchins are abundant and the area is devoid of kelp forests. Where sea otters are present, the urchins are limited by otter predation and kelp forests are abundant. Kelp forests are dependent on sea otters for protection from grazers. The diversity of the sea otter diet reduces competition between benthic grazers and supports greater diversity in those species. The presence of sea otters is believed to be important in the evolution of kelp forest ecosystems.

Global Abundance

10,000 to >1,000,000 individuals

Comments: Estimates from the mid- to late 1980s suggested populations of 6000-7000 in the Kuril Islands, 2000-2500 in the Commander Islands, and 2500-3000 off Kamchatka, giving a total western Pacific population of 10,500-12,500 (Riedman and Estes 1990, Reeves et al. 1992). In the 1980s, the total population from Prince William Sound to the Kuril Islands was about 150,000 (Riedman 1990). For the Aleutian Islands, the minimal population estimate was 8,742 sea otters in 2000 (Doroff et al. 2003).

Alaska had 100,000-150,000 in the mid- to late 1980s (Reeves et al. 1992), and the current population probably also is in this range (USFWS 1995 stock assessment). Prince William Sound population in late 1980s was about 14,000, of which an estimated 2800 were killed as a result of the Exxon Valdez oil spill (Raloff 1993). From an original 402 individuals translocated in the 1960s, the population in southeastern Alaska increased to more than 3500 in five populations by 1987 (Reeves et al. 1992); 1988 estimate was 4520 (See Riedman and Estes 1990).

In 1984, the population off west coast of Vancouver Island, British Columbia, was 345 (descended from 89 that were translocated from Alaska, 1969-1972) (MacAskie 1986); 1987 count was 380 (see Riedman and Estes 1990). In 1995, the minimum number along the coast of British Columbia was 1522, including 135 near Goose Island (Watson et al. 1997).

Otters were transplanted from Alaska to Washington in 1969 and 1970; population increased from 36 to 94 between 1981 and 1987 (Matthews and Moseley 1990); 211 were counted in Washington in July 1989 (Jameson, in Riedman and Estes 1990, Reeves et al. 1992).

See also record for subspecies nereis of California (about 2,505 individuals in 2003).

Males defend contiguous territories from which they exclude other males (Riedman and Estes 1990).

Males may move up to 30-60 miles along coast, females generally stay within area 5-10 miles long. Daily movements generally encompass a few kilometers (Riedman and Estes 1990). Ralls et al. (1996) found that otters in California usually were within 1-2 km of their location on the previous day but often stayed in one place for an extended period then suddenly moved a much greater distance; the area used by individual otters during a single 24-hour period was 7-1166 ha.

Undisturbed populations can increase at about 17-20%/year, although the central California population never has increased at more than 5-7%/year (Riedman and Estes 1990).

Lifespan, longevity, and ageing

Maximum longevity: 27 years (captivity) Observations: There is a delayed implantation and the total gestation time varies from 4 to 12 months. The actual embryonic development takes about 4-5.5 months (Ronald Nowak 2003). It has been suggested that longevity in the wild may be as high as 30 years (Bernhard Grzimek 1990), which is dubious. One wild born female was about 27 years old when she died in captivity (Richard Weigl 2005).

Reproduction

Sea otters have a polygynous mating system. Many males activly defend territories. Disputes are usually settled with splashing and vocal displays, fighting is rare. Males will mate with females that inhabit their territory or seek out estrus females if no territory is established. Males and females bond for the duration of estrus, or 3 days. The male holds the female's head or nose with his jaws during copulation. Visible scars are often present on females from this behavior.

(McShane et. al. 1995; Estes 1980; Nowak 1999)

Mating System: polygynous

Sea otters can reproduce year round. There are peaks of birth in May-June in the Aleutian Islands and in January-March in the California population. Delayed implantation produces varied gestation times. Pregnancy has been reported to be 4-12 months. Females usually give birth about once a year. Orientation of the fetus may be either caudal or cephalic, although cephalic orientation is more common near birth. A single pup is born weighing 1.4-2.3 kg. Twins occur in 2% of births but only one pup can be raised successfully. Pups typically remain with their mother for 5 to 6 months after birth. Females that lose a pup will go into estrus sooner than if their pup had survived. Females reach sexual maturity at 4 years. Males reach sexual maturity at 5 to 6 years, but may not mate until much later.

Females provide all of the parental care for the young. Pups will nurse until weaned, but start to eat solid foods shortly after birth. While the mother is foraging, young will remain on the surface. Pups start diving after two months. Pups learn from their mothers how to forage and what prey items to look for as well as swimming and grooming behaviors. The pup remains dependent on the mother for about 6 to 8 months, but there is considerable variation here also.

Strongly polygynous. Reproduction is weakly seasonal. Births in spring and summer with peak in early summer in Alaska (late May in Prince William Sound); peak December-March (generally late winter) in California. Implantation delayed, gestation about 8-9 months in Alaska, about 4-6 months in California. Young dependent on mother for about 6-7 months in California, 76-333 days (average 170) in Prince William Sound, Alaska. In California, adult females generally give birth to 1 pup every year; females in some areas of Alaska give birth every other year. In California, females sexually mature usually in 3-5 years. In Alaska, 30% of females were sexually mature at age 2, 100% by age 5; annual reproductive rates increased from 22% at age 2 to 78% at age 5 and remained relatively stable (75-88%) through age 15 (Bodkin et al. 1993). Commonly lives 10-15 years; maximum known ages are 23 years for females and 18 years for males.

Barcode data: Enhydra lutris

The following is a representative barcode sequence, the centroid of all available sequences for this species.

There are 3 barcode sequences available from BOLD and GenBank. Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species. See the BOLD taxonomy browser for more complete information about this specimen and other sequences.

AATCGATGATTATTCTCCACAAATCACAAAGACATCGGCACCCTTTACCTTTTATTCGGTGCATGAGCCGGAATGGTAGGCACCGCTCTCAGCCTATTAATCCGTGCTGAATTAGGTCAACCTGGCGCTCTATTAGGGGAT---GACCAGATTTATAATGTTATCGTCACCGCCCACGCATTCGTGATAATTTTCTTTATAGTAATACCAATCATGATCGGTGGGTTTGGAAACTGACTAGTACCCCTAATAATTGGTGCGCCTGACATAGCATTTCCACGAATAAACAATATAAGCTTTTGACTCCTACCCCCCTCCTTTCTACTTCTTCTAGCCTCATCTATGGTAGAAGCGGGTGCAGGAACAGGATGAACCGTATACCCCCCTTTAGCAGGTAATCTAGCACATGCAGGAGCATCGGTAGACCTGACAATTTTTTCTCTACACCTGGCAGGTGTATCGTCCATCCTAGGAGCTATCAATTTTATCACCACTATCATTAACATAAAACCCCCCGCAATATCACAATACCAAACTCCCTTATTCGTGTGATCTGTACTAATTACGGCCGTGCTTTTACTCCTATCTCTACCAGTCTTAGCAGCCGGTATTACTATACTACTTACAGACCGGAATCTGAATACCACCTTTTTTGACCCAGCTGGAGGAGGAGACCCTATTCTATACCAACACTTATTCTGATTCTTCGGACACCCAGAAGTATACATTCTAATTCTGCCTGGATTCGGAATTATCTCACACGTCGTTACATACTACTCAGGAAAGAAAGAACCGTTTGGTTATATAGGAATGGTATGGGCAATAATATCAATTGGCTTCCTAGGCTTTATTGTGTGAGCCCACCACATATTTACTGTAGGTATGGATGTCGATACACGAGCATACTTTACATCAGCCACTATAATCATTGCTATCCCTACAGGGGTAAAAGTATTTAGCTGACTGGCTACTCTACACGGAGGA---AAT-- end --

United States

IUCN Red List Assessment

Red List Category

EN

Endangered

Red List Criteria

A2abe

Version

3.1

Year Assessed

2011

Assessor/s

Doroff, A. & Burdin, A.

Reviewer/s

Hussain, S.A. & Conroy, J.

Contributor/s

Justification

The Sea Otter is considered to be Endangered due its vulnerability to large-scale population declines. The species is believed to have undergone a decline exceeding 50% over the past 30 years (approximately three generations). The world-wide population of Sea Otters decreased to approximately 2,000 animals by the end of the commercial fur trade in 1911 (Kenyon 1969). The population recovered from 11 remnant populations located in Russia (Bering Island, Kamchatka Peninsula, and Kuril Islands) and in the United States (in Alaska (Aleutian Islands, Alaska Peninsula, Kodiak archipelago, and Prince William Sound) and California). The remnant populations were small and widely dispersed, as a result, this species has low genetic diversity (Ralls et al. 1983). Since the 1980s, the species had been recovering in many areas thanks to intensive management and regulatory efforts by several governments. However contemporary issues (oil spills, potential fisheries interactions, predation, and disease events), have either prevented Sea Otter populations from thriving or have caused population declines throughout much of the species range. In the United States, two subspecies of Sea Otters are listed as threatened (E. lutris kenyoni in SW Alaska and E. lutris nereis in California) due to precipitous population declines in Alaska and slow growth (and vulnerability to anthropogenic factors) of a small population in California.

In Alaska, precipitous population declines occurred in the Aleutian Islands beginning in the late 1980s–2005. By 2000, counts of Sea Otters had decreased by 90% with a declining trend through 2005 (Doroff et al. 2003, Estes et al. 2005, Burn et al. 2003). The probable cause of the decline was increased predation by killer whales (Orcinus orca) (Estes et al. 1998). More recent Sea Otters surveys indicate the population trend has increased since 2005, however, counts remain well below carrying capacity for this region (D.M. Burn pers. comm. 2010). Population counts also remain low for the Alaska Peninsula (Burn and Doroff 2005, U.S. Fish and Wildlife Service Stock Assessment Reports). The population in the Kodiak archipelago and lower Cook Inlet appeared stable or increasing during the same period that population declines were documented in the Aleutian Islands and Alaska Peninsula (Kodiak and lower Cook Inlet are part of the Southwest population stock), however, this habitat has not been surveyed since 2004.

Recent studies have found infectious disease to be an important mortality factor in California Sea Otter populations (Conrad et al. 2005, Johnson et al. 2009). Information collected from forensic-level necropsies of dead Sea Otters and sampling of free-ranging Sea Otters indicate a strong link to protozoan parasites, Toxoplasma gondii and Sacrocystis neurona, that are known to breed in cats and opossums (Thomas and Cole 1996, Conrad et al. 2005) thus sources of mortality for the Sea Otter population include land-based factors. Other factors identified as causing significant mortality include acanthocephalan peritonitis, protozoal encephalitis, bacterial and fungal infections (Thomas and Cole 1996).

The situation in the Russian Federation is clearer now. The Sea Otter number on the Commander Islands reached maximum since last 150 years period (A. Burdin and S.V. Zagrebelny pers. comm. 2006). In 2007, the direct count revealed around 8,000 otters in both Bering and Medny Islands. The Commanders Island population of Sea Otter was never so abundant, but in 2008, it was found that the population was on decline. In 2004 the Kuril Islands population of Sea Otter was estimated around 19,000 (Kornev and Korneva 2004), but later count have shown sever decline (up to 40–50% in different locations). Though the causes of such decline are not very clear, the threat due to poaching can’t be ruled out.

Conservation Status

The fur trade depleted sea otters to about 1000-2000 individuals worldwide by 1911 when the International Fur Seal Treaty between the U.S., Russia, Japan, and Great Britain was established. The U.S. Marine Mammal Protection Act in 1972 provided more support for sea otters. Reintroduction along the west coast of North America and protection from hunting has brought the world population up to 100,000-150,000. The population of California sea otters (Enhydra lutris nereis) is listed as threatened under the Endangered Species Act and will remain so until a population of 2650 is recorded for three consecutive years. The current population is about 2200. There are concerns that a single oil spill could wipe out the California sea otter. In 1989, the Exxon Valdez flooded Prince William Sound, Alaska with oil. An estimated 5,000 sea otters were killed as a result. E.l. nereis is listed in appendix 1 of CITES, the other subspecies are in appendix 2. The IUCN lists Enhydra lutris as endangered.

NatureServe Conservation Status

Reasons: Large range in North Pacific; total population has increased to more than 100,000 (430 in Washington); subject to intensive management; vulnerable to oil spills and conflicts with commercial fisheries.

Status

Population

Population

The Sea Otter population thought to have once been 150,000 to 300,000, occurring along the North Pacific from northern Japan to the central Baja Peninsula in Mexico. Its abundance was greatly reduced by human exploitation. Between 1751 and 1911 the distribution was reduced to 13 known remnant populations: two in the Kuril Islands and Kamchatka; one in the Commander Islands; a total of 10 in the following areas: Aleutian Islands (2)and along the Alaska Peninsula (3); Kodiak Island (1), Prince William Sound (1), the Queen Charlotte Islands (1), central California (1), and San Benito Islands (1). However, the Queen Charlotte, Canada and San Benito Island, Mexico remnant Sea Otter populations have died out and likely did not contribute to the recolonization of the species following near extirpation (Kenyon 1969).

Sea Otters currently have established populations in parts of the Russian east coast, Alaska, British Columbia, Washington, and California, and there have been reports of single-animal observations in Mexico and Japan. Population estimates made between 2004 and 2007 give a worldwide total of approximately 106,822 Sea Otters. In Russia, population monitoring has increase for Sea Otters throughout the range and number are about 19,000 are in the Kurils, 2,000 to 3,500 on Kamchatka and another 5,000–5,500 on the Commander Islands. The Sea Otter population in Alaska was estimated at between 100,000 and 125,000 individuals in 1973. By 2006, however, the estimated population had fallen to an estimated 73,000 animals in Alaska. A massive decline in Sea Otter population in the Aleutian Islands accounts for most of the change; the cause of this decline is not known, although orca predation was suspected. The Sea Otter population in Prince William Sound was also hit hard by the Exxon Valdez oil spill, which killed thousands of Sea Otters in 1989. Along the North American coast south of Alaska, the Sea Otter's range is discontinuous. Between 1969 and 1972, 89 Sea Otters were flown or shipped from Alaska to the west coast of Vancouver Island, British Columbia. They established a healthy population, estimated to be over 3,000 as of 2004, and their range is now from Tofino to Cape Scott. In 1989, a separate colony was discovered in the central British Columbia coast. It is not known if this colony, which had a size of about 300 animals in 2004, was founded by transplanted otters or by survivors of the fur trade. In 1969 and 1970, 59 Sea Otters were translocated from Amchitka Island to Washington State. Annual surveys between 2000 and 2004 have recorded between 504 and 743 individuals, and their range is in the Olympic Peninsula from just south of Destruction Island to Pillar Point. California has over 3,000 Sea Otters, descendants of approximately 50 individuals discovered in 1938. The spring 2009 Sea Otter survey counted 2,654 Sea Otters in the central California coast, which is suggestive of a population that is stable or slightly declining; counts are down from an estimated pre-fur trade population of 16,000 (USGS unpublished data). California's Sea Otters are the descendants of a single colony of about 50 southern Sea Otters discovered near Big Sur in 1938; their principal range is now from just south of San Francisco to Santa Barbara County. In the late 1980s, the US Fish and Wildlife Service relocated about 140 California Sea Otters to San Nicolas Island in southern California for establishing a reserve population should the mainland is struck by an oil spill. The San Nicholas population initially shrank as the animals migrated back to the mainland, as of 2005, only 30 Sea Otters remained at San Nicholas, thriving on the abundant prey around the island.

Threats

Major Threats

Oil spills are the greatest anthropogenic threat to Sea Otter (Geraci and Williams 1990). Sea Otters become hypothermic when oiled because oiled Sea Otter fur loses its insulative property and Sea Otters have no blubber layer, oil can be ingested while grooming, leading to gastrointestinal disorders, other ailments and death and volatile components of oil inhaled by Sea Otters can cause lung damage. Estimates of sea otter mortality following the Exxon Valdez spill in Prince William Sound ranged from 2,650 (Garrott et al. 1993) to 3,905 (DeGange et al. 1994).

Significant numbers of Sea Otters drowned in gill and trammel nets in California from the mid-1970s to the early 1980s (Estes 1990). Recent population declines in California’s Sea Otters may be incidental to summer commercial fisheries. Estes et al. (2003) found that Sea Otter mortality was elevated in the summer months and that commercial fin fish landings in the coastal live trap fishery increased. Recent analyses indicated annual Sea Otter carcass recoveries and reported fishery landings were significantly correlated.

Thomas and Cole (1996) found 10% of southern Sea Otters they examined to be emaciated without specific cause of mortality. Severe weather and periodic climatic events such as El Niño can disrupt foraging behaviour and food availability, and increase pup loss. Under these circumstances, Sea Otters may find it difficult to meet their high metabolic needs, leading to malnutrition or starvation. Serious tooth wear in older Sea Otters may also contribute to mortality (Riedman and Estes 1990). Recent studies have found infectious disease to be an important mortality factor in California Sea Otter populations. Around 280 Sea Otters found dead have been linked “to a pair of protozoan parasites, Toxoplasma gondii and Sacrocystis neurona, that are known to breed in cats and opossums (Conrad et al. 2005, Johnson et al. 2009). In Alaska, Streptococcal endocarditis, encephalitis and/or septicemia, referred to as Strep. syndrome has been identified in forensic-level necropies of northern sea otters (Unusual mortality event working group) as well as trauma from boat strikes. Goldstein et al. (2009) found northern sea otters from the Alaska Peninsula, Kodiak and Kachemak Bay area infected with phocine distemper.

Studies in Alaska and Washington and elsewhere have shown that Sea Otter predation on sea urchins may indirectly enhance the growth of kelp and kelp-associated communities. Shellfish are important to commercial, recreational, and tribal fisheries throughout the species range and predation by Sea Otters can be significant and result in localized fisheries and economic issues.

Degree of Threat: B : Moderately threatened throughout its range, communities provide natural resources that when exploited alter the composition and structure of the community over the long-term, but are apparently recoverable

Comments: In various parts of the range, conflicts with commercial fisheries (gill and trammel nets, crab traps) and activities associated with oil and gas exploration, development, and transportation may be the greatest threats. Commercial fisheries are not a threat in Alaska (USFWS 1995 stock assessment). Brody et al. (1996) determined that an oil spill of Exxon Valdez size, occurring at the Monterey Peninsula, California, would kill at least 50% of the total California sea otter population.

In the Aleutian Islands in recent decades, the population declined to a uniformly low density in the archipelago, suggesting a common and geographically widespread cause. These data are in general agreement with the hypothesis of increased predation on sea otters (Doroff et al. 2003). Killer whales presumably shifted their diet to include sea otters after populations of their preferred prey, harbor seals (Phoca vitulina) and Steller sea lions (Eumetopias jubatus), declined.

Threats

Since the 1700s, prior to the commercial fur trade, native peoples throughout the otter's range harvested sea otters for their pelts (2). An intensive commercial fur trade, from 1740 until about 1900, resulted in the sea otter being harvested almost to extinction, and by 1900, the sea otter was so rare that commercial harvesting was forced to cease (6). Sea otters were protected by an international treaty in 1911. Since then, numbers have recovered to an extent, but human activities, especially coastal development and marine pollution, now pose a threat to the sea otter (6). In 1989, hundreds, and possibly thousands, of sea otters were killed as a direct result of the Exxon Valdez oil spill in Prince William Sound in Alaska (4). The possibility of another major oil spill poses a continual threat to the sea otter, and could have devastating consequences. Additional threats include entanglement in fishing gear, particularly gill nets, and competition with commercial fisheries for food (6). In the central Aleutian Islands, Alaska, sea otters have declined by as much as 90 percent (4). Evidence indicates that this drastic decline is the result of increased predation by killer whales, which have switched to consuming more sea otters following the collapse of Steller's sea lion and harbour seal populations in the region (4).

Conservation Actions

Conservation Actions

Enhydra lutris nereis is listed on CITES Appendix I. All other populations are included in CITES Appendix II. In Canada, Sea Otters are protected and managed under the Species at Risk Act. In the United States, Sea Otters are protected by the Marine Mammal Protection Act of 1972 (MMPA) and in Southwest Alaska and California, the Endangered Species Act of 1973 (ESA). The US Fish and Wildlife Service (Service) is the federal agency responsible for their conservation and management. The ESA also makes it illegal to buy, sell or possess any part of endangered species or items made from them. However, both the ESA and the Act allow for coastal Native people in Alaska to harvest Sea Otters for personal use, trade, barter, and the development of cottage industry. Native subsistence harvest of Sea Otters is monitored by the Service through a Marking, Tagging and Reporting program. The Service and Native organizations conduct joint population surveys and dialog on important conservations issues. The MMPA also mandates that efforts must be made to recover the species, which means creating and implementing a plan for returning them to healthy population levels.

Despite protection and various conservation measures, the southern Sea Otter population has been slow to recover. In 1994, the Service developed a Conservation Plan for northern Sea Otters in Alaska with the aim of managing human activities that hinder Sea Otter population recovery or sustainability. When a significant portion of the species range is stable and healthy, this will facilitate removing the species from the List of Endangered and Threatened Wildlife. Many of the conservation actions in the 1994 Plan have been completed, however, the population declines in the Aleutian Islands were unanticipated and new health risks are being identified that may limit population recovery. There have been several successful reintroduction attempts along the west coast of North America, restoring this highly appealing animal to much of its former range.

Restoration Potential: Recovery potential is high if environmental conditions are favorable. In Alaska, otters at the leading edge of an expanding population in an area with abundant food resources and protected water exhibited high adult survival rate, high reproductive rate, and high preweaning survival (Monson and DeGange 1995). Human harvest was the primary source of known mortality of adults.

Management Requirements: See the 1996 Endangered Species Update 13(12) for 20 articles dealing with sea otter conservation and management.

Brody et al. (1996) reviewed the EXXON VALDEZ oil spill and concluded that efforts to rehabilitate otters should be discontinued 20-30 days after a spill.

Draft revised recovery plan for California populations was available in February 2000 (contact U.S. Fish and Wildlife Service, Ventura, California).

Conservation

The sea otter is legally protected in the United States under the Marine Mammal Protection Act and in Canada sea otters are protected under the Species at Risk Act (10). Despite protection and various conservation measures, the Californian population has been slow to recover; a new Recovery Plan by the U.S. Fish and Wildlife Service was currently being developed with the aim of managing damaging human activities to enable the population to recover to a point where it can be removed from the List of Endangered and Threatened Wildlife (11). There have been several successful reintroduction attempts along the west coast of North America, restoring this highly appealing animal to much of its former range (2).

NatureServe Explorer

Animalia - Craniata - Mammalia - Carnivora - Mustelidae - Enhydra - Lidicker and McCollum (1997) examined allozyme variation and found that despite historical population depletion, otters from California have suffered only a small loss in genetic variability. MtDNA data also indiciate that population bottlenecks probably did not result in major losses of genetic variation in individual populations or the species as a whole (Cronin et al. 1996). However, based on microstatellite DNA and mtDNA, Larson et al. (2002) reported that the levels of genetic diversity observed within sea otter populations were relatively low when compared with other mammals and may be the result of fur trade exploitation.

Diet varies according to location; often dominated by benthic invertebrates. Sea urchins, crabs, and a variety of molluscs are principal foods, but fish are important food items at high population densities. Forages usually at depths of less than 20 m. Uses rocks or other hard objects as tools to break exoskeletons of invertebrate prey. Diets and patterns of foraging behavior may be highly individualized (Riedman and Estes 1990).

Reproduction Comments:

Strongly polygynous. Reproduction is weakly seasonal. Births in spring and summer with peak in early summer in Alaska (late May in Prince William Sound); peak December-March (generally late winter) in California. Implantation delayed, gestation about 8-9 months in Alaska, about 4-6 months in California. Young dependent on mother for about 6-7 months in California, 76-333 days (average 170) in Prince William Sound, Alaska. In California, adult females generally give birth to 1 pup every year; females in some areas of Alaska give birth every other year. In California, females sexually mature usually in 3-5 years. In Alaska, 30% of females were sexually mature at age 2, 100% by age 5; annual reproductive rates increased from 22% at age 2 to 78% at age 5 and remained relatively stable (75-88%) through age 15 (Bodkin et al. 1993). Commonly lives 10-15 years; maximum known ages are 23 years for females and 18 years for males.

Males defend contiguous territories from which they exclude other males (Riedman and Estes 1990).

Males may move up to 30-60 miles along coast, females generally stay within area 5-10 miles long. Daily movements generally encompass a few kilometers (Riedman and Estes 1990). Ralls et al. (1996) found that otters in California usually were within 1-2 km of their location on the previous day but often stayed in one place for an extended period then suddenly moved a much greater distance; the area used by individual otters during a single 24-hour period was 7-1166 ha.

Undisturbed populations can increase at about 17-20%/year, although the central California population never has increased at more than 5-7%/year (Riedman and Estes 1990).